1. Field of the Invention
The present invention relates to a method of manufacturing a liquid discharge head for generating droplets of a recording liquid used in an ink-jet recording system and a liquid discharge head obtained by this method. More particularly, the present invention relates to a shape of an ink channel which provides stable discharge of minute droplets for enabling high image quality and achieves high speed recording, and to a method of manufacturing a head.
Furthermore, the present invention relates to an ink-jet head whose ink discharge property is improved in accordance with the method of manufacturing the ink-jet head.
2. Description of the Related Art
A liquid discharge head applied to an ink-jet recording method (liquid discharge recording method) in which recording is performed by discharging a recording liquid such as ink is generally provided with liquid channels, liquid discharge energy generating parts which are arranged in a part of each liquid channel, and fine recording liquid discharge ports (hereinafter referred to as “orifices”) for discharging the liquid in the liquid channel by thermal energy of the liquid discharge energy generating parts. As conventional methods of manufacturing such a liquid discharge recording head as the above, there have been known a manufacturing method including steps of forming through holes for ink supply on an element substrate having thereon heaters generating thermal energy for discharging a liquid, driver circuits driving these heaters, or the like, followed by performing patterning to form walls of an ink channel using a photosensitive negative resist, and subsequently joining the patterned substrate to a plate on which is formed ink discharge ports by electroforming or excimer laser machining (e.g., U.S. Pat. No. 6,179,413, or the like), and also a manufacturing method including steps of preparing an element substrate formed in the same manner as in the above method, and machining a resin film (polyimide is preferably used in general) coated with an adhesive layer to form an ink channel and ink discharge ports by excimer laser, and subsequently joining the machined liquid channel structure plate to the element substrate through thermo-compression bonding (e.g., U.S. Pat. No. 6,158,843, or the like).
In the ink-jet head manufactured according to these methods, a distance between the heater and the discharge port which exerts an influence on an discharge amount must be as short as possible in order to enable the discharge of minute droplets for achieving high image quality recording. Therefore, there is a need to lower a height of the ink channel, or to reduce the size of a discharge chamber which is a part of the ink channel and is a bubble production chamber adjacent to the liquid discharge energy generating part, or also to reduce the size of the discharge port. That is, in order to enable the discharge of minute droplets by the head manufactured according to those methods, it is required to make the liquid channel structure laminated on a substrate thinner. However, there is extreme difficulty in precisely machining such a thin liquid channel structure plate and joining thereto a substrate.
In order to solve problems residing in those methods, Japanese Patent Publication No. 6-45242 discloses a method of manufacturing an ink-jet head, including steps of patterning a mold of an ink channel using a photosensitive material on a substrate on which is formed liquid discharge energy generating elements, coating a coating resin layer on the substrate so as to cover the mold pattern, forming ink discharge ports to be communicated with the mold of the ink channel on the coating resin layer, thereafter removing the photosensitive material used to form the mold (hereinafter abbreviated as “casting”). As the photosensitive material used in this method of manufacturing the head, a positive type resist is used in terms of removability. According to this method, application of a photolithography technique in a semiconductor process allows highly precise and fine machining in forming discharge ports and the like. This method adopting such a method of manufacturing semiconductors, however, basically limits variations of a shape in the vicinity of the ink channel and discharge ports to those only in a two-dimensional direction parallel to an element substrate. This means that the use of the photosensitive material for the mold of the ink channel and discharge ports is made impossible to form a partially multilayered photosensitive material layer, so that a desired pattern having differences in a height direction of the mold of the ink channel and the like may not be obtained (the shape in a height direction from the element substrate is uniformly restricted). This may result in a problem when designing ink channels for attaining high speed, stable discharge.
Japanese Patent Application Laid-Open No. 10-291317 discloses that, in excimer laser machining for a liquid channel structure, by partially changing opacity of a laser mask and controlling a machining depth in a resin film, variations in shape of an ink channel are realized in a three-dimensional direction which includes an in-plane direction parallel to an element substrate and a height direction from the element substrate. The depth direction can thus basically be controlled by laser machining, however, the excimer laser used in these machining is different from that used in an exposing process of semiconductors and requires a high luminance laser over a wide range, therefore it is extremely difficult to suppress dispersion in illuminance within a laser irradiated surface and to realize stable laser illuminance. Particularly in an ink-jet head offering a high quality image, non-uniform discharge properties due to variations in a machining shape among respective discharge nozzles are recognized as unevenness in a printed image, it is therefore highly required to realize the enhancement of machining accuracy.
Moreover, there is often the case that minute patterns cannot be formed due to tapers on a laser machining surface.
In Japanese Patent Application Laid-Open No. 4-216952, disclosed is a method of forming a first layer of negative resist on a substrate and thereafter forming a latent image of a desired pattern, coating a second layer of negative resist on the first layer and thereafter forming a latent image of a desired pattern only on the second layer, and in the end developing pattern latent images for each upper and lower layer, wherein these two layers of upper and lower negative resists have mutually different photosensitive wavelength ranges such that both upper and lower negative resists are sensitive to ultraviolet (UV), or that the negative upper resist is sensitive to ultraviolet (UV) and the negative lower resist is sensitive to an ionizing radiation including Deep UV, electron rays, X rays, or the like. According to this method, by using two layers of upper and lower negative resists having mutually different photosensitive wavelength ranges, pattern latent images can be formed, which have a difference in those shapes not only in a direction parallel to a substrate and also in a height direction from the substrate.
The inventor et al. of the present invention have earnestly studied to apply the technique disclosed in Japanese Patent Application Laid-Open No. 4-216952 to the above described casting. That is, it has been expected that the application of the technique disclosed therein to the formation of a mold for ink channels according to casting allows local changes in a height of a positive resist used as the mold of ink channels and the like.
An attempt has actually been made such that, as a photoresist removable by dissolving and sensitive to ultraviolet (UV) as described in Japanese Patent Application Laid-Open No. 4-216952, an alkaline developing positive photoresist composed of a mixture of an alkali-soluble resin (novolak resin or polyvinylphenol) and a naphthoquinone diazide derivative is used, and as a photoresist sensitive to an ionizing radiation, polymethyl isopropenyl ketone (PMIPK) is used, so as to form a mold having upper and lower patterns mutually different relative to a substrate. However, the alkaline developing positive photoresist is immediately dissolved in a developing solution for PMIPK, so that different patterns for two layers fail to be formed.
Therefore, another attempt has been made to discover a preferable combination of upper and lower layers of positive photosensitive materials capable of forming a mold pattern having a difference of shapes in a height direction relative to a substrate according to casting.
The present invention is designed in consideration of the above-mentioned various problems and an object thereof is to provide a liquid discharge head which is inexpensive, precise, and highly reliable, and a method of manufacturing the liquid discharge head.
The present invention relates more particularly to an ink channel shape which allows refilling of ink while rapidly suppressing meniscus oscillation by suitably adjusting a three-dimensional shape of an ink channel, and a method of manufacturing a liquid discharge head provided therewith.
Another object of the present invention is to provide a novel method of manufacturing a liquid discharge head, capable of producing a liquid discharge head having a structure in which a liquid channel is formed precisely and accurately, and machined finely in excellent yield.
Still another object of the present invention is to provide a novel method of manufacturing a liquid discharge head, capable of producing a liquid discharge head with less mutual effect to a recording liquid which is excellent in mechanical strength as well as in chemical tolerance.